1. Field of the Invention
The present invention relates to an image processing device and a method for operating an endoscope system, for performing diagnoses based on observation of a ductal structure and the like in a human body.
2. Description Related to the Prior Art
Diagnoses using endoscope systems are widely performed in current medical care. The endoscope system comprises a light source device, an electronic endoscope, and a processor device. Observation of a human body cavity is performed using the endoscope system. Such observation includes screening observation and magnified observation. In the screening observation, a potential lesion (site with a high possibility of being a lesion) such as a brownish area or redness is detected from a far view. The magnified observation is performed in a case where the potential lesion is detected. In the magnified observation, the endoscope zooms in on the potential lesion. Thereby the potential lesion is magnified and examined. Diagnosis is performed based on the observation of a ductal structure.
In the magnified observation of the ductal structure, the contrast of the ductal structure S is low in a normal image (an image captured with the illumination of the white light). It is difficult to interpret the state of the ductal structure S. In this case, a dye such as an indigo is sprayed. The dye deposits on pits of the ductal structure S. Thereby the contrast of the ductal structure S is improved. The sprayed dye makes the ductal structure S conspicuous, allowing interpretation of the state of the ductal structure S.
The ductal structure S is enhanced with a white color in a displayed image by illuminating the ductal structure S with blue narrowband light of narrowband wavelengths in a blue region. This is due to the fact that the narrowband light tends to be reflected around a surface layer of a mucous membrane. The contrast of the ductal structure S improves in a blue narrowband image captured with the illumination of the blue narrowband light, allowing the interpretation of the state of the ductal structure S (see Japanese Patent No. 3607857).
In narrowband light observation using the blue narrowband light, the structure of the ductal structure S is enhanced without spraying the dye. Washing of the dye is unnecessary, which reduces the burden of a doctor. The ductal structure S in the narrowband light observation is displayed in whitish colors. The dye-sprayed ductal structure S is displayed in bluish colors. The color of the ductal structure S in the narrowband light observation is totally different from the color of the dye-sprayed ductal structure S when displayed. The doctor who is accustomed to the dye observation has difficulties in observing the ductal structure S displayed in a color different from that of the dye such as the indigo.
For this reason, it is desirable to display the ductal structure S in colors close to the color of the dye such as the indigo, even in the narrowband light observation. For example, in the Japanese Patent No. 3607857, the blue narrowband image is assigned to RGB channels (ch) of a monitor. A weighting factor for the B ch is made greater than those for the G ch and R ch. Thereby the ductal structure S is displayed in colors similar to those of the dye-sprayed one. In this case, however, not only the ductal structure S but also the capillary vessels are displayed in indigo colors. A difference between the ductal structure S and the capillary vessels is not obvious and cannot be enhanced.
The ductal structure displayed brightly in white color may be partially darkened by a tone reversal process disclosed in Japanese Patent Laid-Open Publication No. 2009-066147 and Japanese Patent Nos. 4451460, 3572304, and 3559755. Thereby the ductal structure is made conspicuous in a manner similar to the indigo spraying. However, the tone reversal process is applied to every pixel in the image. The tone of a vascular structure is reversed in addition to that of the ductal structure.
For example, when the tone reversal process is performed on a narrowband image (an image in which both the ductal structure S and the capillary vessels V are enhanced in the display due to the application of the blue narrowband light) produced in the narrowband light observation, the capillary vessels V are highlighted and as conspicuous as the ductal structure S as shown by a reversed narrowband image shown in FIG. 24A. In FIG. 24B, black thick lines are added to the image of FIG. 24A displayed on the monitor, to indicate the ductal structure S. The conspicuous blood vessels impair visual recognition properties of the ductal structure S and make it difficult to accurately interpret the state of the ductal structure S. Thus, it is necessary to enhance the display of the ductal structure without making the blood vessels conspicuous.
Note that the Japanese Patent No. 3572304 discloses that the blood vessels are clearly displayed by the tone reversal process. However, neither of the above-mentioned documents including the Japanese Patent No. 3572304 touches upon displaying the ductal structure with high clarity in the narrowband light observation and enhancing the ductal structure in the display without making the blood vessels conspicuous.